Method and apparatus for coating ferrous metal with aluminum



Aug. 30, 1960 H. w. SEYMOUR 2,950,991 7 METHOD AND APPARATUS FOR COATINGFERROUS METAL WITH ALUMINUM Filed April 30, 1959 High Prasuro AtomizinqAir Water High Pressure ir Supply Water Supply.

INVENTOR. Harvey W. Seymour BY ATTORNEYS Q L L ,4 t

Patented Aug. 36,196il ice WTHOD AND APPARATUS FOR COATING FERROUS METALWETH ALUMKNUM Harvey W. Seymour, Belle Vernon, Pa., assignorto Amen ieanChm & Cable Company, Inc., a corporation of New York Filed Apr. 30,1959, Ser. No. 810,174

1% Claims. (Q1. 117-119A) This invention relates to the manufacture ofalumihum-coated ferrous metal articles, and is particularly directed toan improved method and improved apparatus for aluminum coating by a hotdip procedure. This application is a continuation in part of mycopending application Serial No. 544,215, filed November 1, 1955, nowabandoned.

The invention provides an improved method and improved apparatus forrapid cooling and congealing of the aluminum coating promptly uponemersion of the ferrous metal article from the molten aluminum bath,Without distorting or roughening the coating, and it is a particularobject of the invention to provide for such cooling in a continuousaluminum coating operation for coating ferrous metal wire, rod, Sheet,strip, and other articles. The scope of the invention, however, is notconfined to continuous operation, for it may be applied to batchoperations as well.

Numerous proposals have been made heretofore to form a protectivecoating of aluminum on ferrous metal articles by dipping the article inmolten aluminum and then withdrawing the aluminum coated article fromthe molten bath. A method which is particularly efiective for thusforming an adherent aluminum coating, free from pinholes and similardefects, is described in U.S. Patent No. 2,686,355 to Harald Lundin. TheLundin method is characterized by the use of a flux comprising afluoride compound of zirconium or titanium to promote formation of atightly adherent continuous aluminum coating on the steel or otherferrous metal article. Other hot dip methods, some using other fluxcompositions, and some using no fluxes at all, have also been proposedand used with varying degrees of success to form aluminum coatings onsteel articles.

Much difficulty has been encountered heretofore in forming adequatelysmooth and adequately thick aluminum coatings, possessing adequateductility, by hot dip methods, particularly on wire and strip of theheavier gauges. The temperature at which the molten aluminum bath mustbe held in the hot dip coating method is high enough to have a stressrelief annealing effect on ferrous metal articles immersed therein. Eventhough the time of immersion is short, the ferrous metal shape generallyis heated substantially throughout its entire cross-sectional area tothe temperature of the molten aluminum. Consequently it is frequentlydesirable to subject the freshly coated ferrous metal to cold working todevelop the hardness and tensile strength that may be required forspecific applications. Cold working results in reducing the thickness ofthe aluminum coating, and unless the freshly formed aluminum coating isquite thick, the coating on the cold worked product will be too thin tomeet certain commercial requirements.

Heavy gauge wires, sheets, etc., which have been heated to thetemperature of the molten aluminum during formation of the aluminumcoating do not cool rapidly in air, because of the considerable mass ofthe ferrous metal. It has been observed that an appreciable period oftime is required for the ferrous metal to cool in air to a temperaturebelow that at Which the aluminum coating ceases to flow. This isparticularly true in high speed continuous coating operations, for suchoperations unavoidably result in subjecting the moving wire or sheet tovibration which tends to induce flow of the coating metal even when thelatter is in a mushy or semi-solid state. Flow of the aluminum coatingon the ferrous metal results in reduction in the thickness of thealuminum coating by drainage of coating metal back into the aluminumbath; and it also commonly results in the formation of coatings ofuneven thickness and of rough surface.

Another objectionable effect which is traceable to slow cooling of theferrous metal is that the aluminum coating thereon displays a markedlack of ductility. Such lack of ductility results from an excessivethickness of a brittle intermetallic iron-aluminum compound which formsby interdifiusion of the aluminum coating and the ferrous metal base.The amount of such compound which is formed and hence the thickness ofthe brittle layer depends on the length of time during which thealuminum and the ferrous metal are held at an elevated temperature.Since the relatively heavy gauges of steel wire and sheet, and othercorrespondingly heavy articles, cool only slowly to a temperature belowthat at which the brittle intermetallic compound forms, the coating onsuch wires, sheets and otherarticles is subject to cracking and peelingwhen the article undergoes substantial deformation.

Other difficulties heretofore encountered in hot dip aluminizing methodsare due to the rather coarse grain structure of the coating layer andthe accumulation of iron in the coating bath. These factors have beenfound to be related to each other and to the composition of the aluminumbath. The bath may contain substantial silicon (say about 2.5%) toinhibit formation of the brittle aluminum-iron layer between the coatingand the ferrous metal base. However, as iron builds. up in the bath(from the ferrous metal passed through it), an undesirable compound ofiron, aluminum and silicon, in a form which adversely afiects coatingductility and adherence, occurs in the coating. Thus, steel wire whichhas been aluminized by passage through an aluminum bath containing about2.5% silicon and in which considerable iron has accumulated, and whichhas then been air-cooled, is found to have a coating comprising rathercoarse particles of an aluminum-silicon-iron compound in a matrix ofaluminum-silicon. The coarse segregated aluminum-iron-silicon compoundsubstantially impairs the adherence and ductility of the coating. Tokeep the adverse effect of such segregations Within reasonable bounds,it has been necessary heretofore to maintain the iron content of thealuminum bath at a low value (generally below 1%) either by makingperiodic additions of pure aluminum-silicon alloy, or by discarding itwhen the iron content has become too high.

Owing to the foregoing circumstances, much difficulty has beenencountered heretofore in producing aluminumcoated ferrous metal wiresand sheets of good quality in any but thin gauges. Such success as hasbeen attained with the heavier gauges has been under special manufacturing conditions which have in general resulted in low productionoutput and correspondingly high manufacturing costs.

The present invention provides an improved method and improved apparatusfor producing aluminum-coated ferrous metal articles by a hot dip methodwhich avoids the disadvantages heretofore encountered. By means of theinvention it is possible to produce adequately thick and smooth aluminumcoatings by hot dip methods on even heavy gauges of Wires and sheets,and yet the ironaluminum inter-facial layer is thin enough so that thecoatings possess adequate ductility to withstand severe mechanicaldeformation without cracking or peeling. Moreover, the invention leadsto an improved coating grain structure in which theiron-aluminum-silicon compound is uniformly distributed as smallspheroids through the aluminum-silicon matrix, in which form thecompound has relatively little effect on coating ductility andadherence. Consequently the invention makes it possible to tolerate upto 2% or even more of iron in the aluminum bath. These results areattainable in accordance with the invention at high coating speeds andwith correspondingly low manufacturing costs.

The foregoing advantages are attained in accordance with this inventionby subjecting the aluminum coated article, immediately upon itswithdrawal from the bath of molten aluminum, to a quenching operating ina dense mist of liquid coolant droplets. It has been proposed heretoforeto quench articles that have been coated with aluminum by a hot dipmethod, but the conventional quenchingprocedures which such proposalshave entailed are unsatisfactory because they result in seriousroughening of the aluminum coating. For example, if an ordinary streamor spray of coarse drops of water are directed at the aluminum coatedarticle before the aluminum coating thereon has fully solidified, theimpact of the liquid coolant on the aluminum coating deforms anddistorts the aluminum coating and congeals it in the distorted form, sothat the article is objectionably roughened. Quenching with a blast ofair or other gaseous coolant behaves similarly. We have found, however,that very rapid and effective quenching of the aluminum coating can beachieved by means of a dense mist of exceedingly fine liquid coolantdroplets which impinge on the aluminum coated article at low velocity.Quenching in this fashion results in cooling the aluminum coating almostas rapidly as conventional cooling with a heavy stream or spray ofliquid coolant, but does so without impairing the surface smoothness ofthe aluminum coating.

Briefly stated, the invention provides, in a method for coating aferrous metal shape with aluminum by immersing the shape in a bath ofmolten aluminum and then withdrawing the shape from the bath with acoating of molten aluminum adhering thereto, the improvement whichcomprises introducing the coated shape immediately upon withdrawal fromthe aluminum bath and while the aluminum coating thereon is still fluidinto direct contact with a dense mist of liquid coolant. The mistcomprises a gaseous suspension of very finely divided coolant droplets,and is characterized by (i) very fine particle size (ii) low particlevelocity, and (iii) high particle density. The particle size of thedroplets forming the mist are sufficiently small so that settlementthereof from. suspension is negligibly slow even in a quiet atmosphereand does not occur to any substantial extent in a moderately turbulentatmosphere. The velocity with which the droplets impinge on the aluminumcoated shape is sufficiently low so that substantially no deformation ofthe aluminum coating thereon, even while it is still fluid, is causedthereby. The density of the mist is at least great enough to cool analuminum coated steel wire 0.1 inch in diameter from 1250 F. to below900 F. in less than fifteen seconds; and preferably it is great enoughto cool whatever article is being coated (usually an articlesubstantially more massive than a wire 01 inch in diameter) to below1000 F., or better, to below 900 F., in less than one half minute. As aresult, the aluminum coating is quenched and congealed before flow ofthe molten coating metal can result in a coating having substantialirregularities in thickness and surface smoothness, and in a mannerwhich itself does not contribute to deforming or roughening the coating.Preferably the coated shape is maintained in contact with the mistcoolant until its temperature has been reduced to below 1000 F., and

advantageously to below 900 F., so that growth of brittle iron-aluminumalloy by interdiifusion of the coating and the ferrous metal isminimized.

The liquid coolant employed in accordance with the invention is mostadvantageously water, and is delivered into direct contact with thefreshly coated ferrous metal in the form of a mist of fine liquid waterdroplets. The term mist is used herein in its customary sense to mean asuspension of very fine water or other coolant droplets in air or othergaseous suspending medium, in which the liquid droplets are larger thanat present in a fog so that there is some tendency for settlement of thedroplet particles to occur in a quiet atmosphere, but in which thecoolant droplets are not large enough for the fairly rapid settlementthat characterizes a gentle rain.

Apparatus according to the invention for coating ferrous metal wire,rod, sheet, strip, and other articles comprises a vessel for containinga bath of molten aluminum, and means for continuously passing sucharticle through said bath and for withdrawing the article upwardly fromthe bath in a substantially vertical direction. Spray nozzles aredirected at the vertical path of travel of the article immediately abovesaid vessel,

so that promptly upon emergence of the article from the bath and whilethe aluminum coating thereon is still fluid, the article enters the zonecovered by spray from said nozzles. The lowermost of the nozzles isdirected at the path of travel of the article in the region immediatelyabove said vessel and the uppermost of the nozzles is directed at saidpath of travel at a substantial distance above said vessel, and theintermediate nozzles are spaced so that substantially the entire lengthof said path of travel between the lowermost and uppermost nozzles iscovered by spray therefrom. However, it is desirable for the nozzles tobe so arranged that there is substantially no overlap of the spraydelivered from one nozzle with the spray delivered from an adjacentnozzle where said sprays meet the path of travel of the aluminum coatedarticle. Means are of course provided for delivering a liquid coolant tosaid spray nozzles, and means connect the nozzles with a source ofatomizing gas under pressure, whereby the coolant may be discharged fromthe nozzles in the form of a mist of particles so small that settlementthereof from gaseous suspension is negligibly slow. With such apparatusthe coating is quenched and congealed before fiow thereof on thecontinuously moving ferrous article can impart substantialirregularities to the thickness and surface smoothness of the coating.

An advantageous embodiment of the invention is described below withreference to the single figure of the accompanying drawing. The drawingshows in schematic elevation, and partially in section, a form ofapparatus according to the invention which is particularly well suitedfor coating one or more wires by the method of the invention.

The apparatus shown in the accompanying drawing is particularly designedfor continuously coating a numberof wires W with aluminum in accordancewith the invention. Although only one wire W is shown in the elevationalview of the drawing, it is of course evident that a group of wires canbe arranged in fairly closely spaced relation in planes perpendicular tothe plane of the drawing and can be passed through the apparatussimultaneously.

The apparatus shown comprises a pot furnace-10 of more or lessconventional design, which contains a bath of molten aluminum 11.Conventional heating means (for example an induction heating assembly)provide for maintaining the aluminum molten and at the temperaturerequired for the coating operation.

' A sinker roll 12 is mounted inthe furnace pot well below the surfaceof the molten aluminum bath. The sinker roll is supported at each end ina bearing carried by a'bracket'arm 3.3, the upper end 14 of which issecured to the upper side edge of the pot and the lower end of whichextends down into the pot to beneath the surface of the molten aluminum.The wire W travels, as indicated by the arrows, downwardly into the bathof molten aluminum, around the sinker roll 12, and thence verticallyupward from the pot.

Adjacent the path of the vertically ascending wire is a frameworkcomprising one or more vertical columns 15. This framework carries asupporting structure of angle irons 16 on which a plurality of spraynozzle assemblies 17a, 17b, 18a, 18b, capable of producing a mist ofvery fine coolant droplets in gaseous suspension, are supported invertically spaced array, directed substantially toward the path of wiretravel. Spray nozzle assemblies of the character used in paint sprayingoperations, and capable of producing a mist as fine as a paint spraymist, are well suited for use as the nozzle assemblies. Although thespray nozzle assemblies are all identical, the nozzles 17 in the lowerhalf of the array are connected in one operating group, and the nozzles18 in the upper half of the array are connected in a separately operatedgroup. This arrangement of the nozzles in two opertaing groups isprimarily for operating flexibility and convenience.

Liquid water is delivered to each of the nozzles 17a, 17b in the lowergroup through a water header 19, and compressed air for atomizing thewater and delivering it from the nozzle assemblies in the form of aspray is supplied to each of these nozzle assemblies through anatomizing air header 26. Additionally, compressed air for actuating thecontrol mechanism of the nozzles, by which the spray from the nozzles isturned On and off, is delivered to each nozzle through a control airheader 21. Water is supplied to the water header 19 from a water supplymain 22 through manual shut-0E Valves 23 and 24, and through a pressureregulator valve 25. A water pressure gauge 26 is provided to show thepressure of water entering the header 19. Compressed air is supplied tothe two compressed air headers 20 and 21 from a high pressure air supplymain 27 through a manual shut-off valve 28 and a commercial airtransformer 29 which includes pressure regulator valves and pressuregauges to show the pressure at which compressed air is supplied to theheaders. The admission of compressed air into the control air header 21is governed by a quick acting control valve 30, by operation of whichthe spray nozzles 17 can be rapidly turned on or oif. The air and watercontrols for the lower group of spray nozzles 17 are advantageouslygrouped at a single control panel 31.

Similarly, water is supplied to the spray nozzles 18 in the upper groupthrough a water header 19a, and air for projecting an atomized spray ofwater from the nozzles is delivered through an atomizing air header 29a.Compressed air for actuating the nozzle shut-ofif mechanism is suppliedto each nozzle through a control air header 21a. Water is delivered tothe water header 19a from the main 22, and compressed air is supplied tothe air headers 24M and 21a from the high pressure air main 27, throughcontrol mechanism of the same character as is employed in conjunctionwith the nozzles 17 of the lower group. The controls for the uppergroup, like the controls for the lower group of nozzles, are forconvenience trouped at a single control panel 32. It is advantageous ofcourse for the two control panels 31 and 32 to be located directlyadjacent to one another.

As indicated above, the nozzles 17, 18 are arranged along the path ofvertical travel of the Wire W as it emerges from the molten aluminum inthe pot 10. The angular diameter of the spray cones delivered from thenozzles is preferably great enough so that the sprays from each adjacentpair of nozzles merge together just before reaching the path of wiretravel. Thereby the entire path of wire travel is blanketed with thespray of water droplets emerging from the nozzles, but there is nosubstantial overlap of the spray from one nozzle with that from anadjacent nozzle at the path of travel of the Wire W. The lowermostnozzle 17a is positioned closely adjacent the upper'edge of the potfurnace 10, so that the wire W enters the zone covered by the watersprays promptly after its emergence from the bath 11 of molten aluminum.The uppermost nozzle 18 is located a substantial distance above themolten aluminum so as to provide a spray zone of sulficient lengthtoinsure adequate cooling of the wire even when it is passed through theapparatus at its maximum rate of travel.

An arrangement of splashboards 33 is positioned adjacent the path oftravel of the vertically moving wire on the side thereof opposite thesprays 17, 18. The Water droplets in the mist projected from the sprayswhich pass by the Wire W impinge on the splashboards, coalesce intolarger drops, and drain downwardly into a pan 34 which is supported justabove the pct 10. Drainage water collecting in the pan 34 is carriedaway through a drain pipe 35.

In order to damp out oscillations of the wire W as it moves verticallyupwardly from the pct 10, a damping roll 36 is provided. The dampingroll is supported at each end in a bearing carried by a bracket arm 37which projects from the column 15, and it is held thereby in lightpressure contact with the upwardly moving wire. The damping roll 36should of course be positioned far enough above the pot 10 so that thealuminum coating on the wire is frozen hard before coming in contactwith it.

A head sheave 38 is mounted at the upper end of the supporting structurecarried by the column 15, in position to receive the Wire W at the upperend of its path of vertical travel. The head sheave 38 overlies one endof a quench tank 39. A sinker sheave 40 is mounted adjacent the centerportion of the quench tank, and a takeout sheave 41 is mounted adjacentthe end thereof remote from the head sheave. The Wire W is carriedaround the head sheave 38, thence under the sinker sheave 40, andfinally over the take-out sheave 41, whence it passes to a take-up reel.

Water is delivered into the quench tank 39 through an inlet pipe 42 involume sufficient to maintain the tank substantially full of water. Adrain stand pipe 43 is provided to prevent the quench tank fromoverflowing. The wire W, after passing over the head sheave 38, iscarried by the sinker sheave to beneath the surface of the body of waterin the quench tank, thereby to effect final cooling of the wire to adesirably low temperature.

Operation of the above-described apparatus is as follows: The wire W tobe coated with aluminum is passed continuously into the bath of moltenaluminum 11, under the sinker roll 12, and thence vertically upwardlyand out of the bath. Promptly after the wire emerges from the bath itenters a dense mist of water droplets directed toward its path of travelby the nozzles 17, 18. The direct contact thus established between thehot wire with its fresh still-fluid aluminum coating and the liquidwater droplets of the mist results in quick quenching and congealing ofthe aluminum coating. M

The use of a coolant mist of very fine particles which impinge at lowvelocity on the aluminum coated article, but which are present in highdensity, is a particular feature of the invention. The mist particlesare, as stated above, of such small size that they settle but slowly instill air and hardly at all if the air is moderately turbulent. Such amist is created by atomizing the water with air at quite high presssure(say 75 to pounds per square inch) as it emerges from the spray nozzles,and its velocity at the nozzle is high. However, the wide angle of thespray cone and the great increase in its cross-sectional area at thepath of wire travel as compared with the nozzle aperture results in acorrespondingly low impingement velocity of the mist against the wire.The velocity of the spray, by the time it reaches the path of travel ofthe wire, therefore is sufficiently low so that neither the air nor thesmall water droplets of the mist impinge on the wire with sufiicientforce to cause any objectionable physical distortion of the aluminumcoating before it freezes.

The density of the water particles in the mist (ie the number ofparticles per unit volume of air) can best be specified in terms of thecooling power of the mist. For effectively rapid cooling of the aluminumcoated article, the density of water particles in the mist when it comesin contact with the article should be at least sufficient to cool acontinuously advancing aluminum coated wire 0.1 inch in diameter from atemperature of 1250 F. to below 900 F. in less than fifteen seconds. Amist of such density is quite effective for cooling small wires (up tosay inch or slightly larger). For relatively heavier articles a moredense mist is advantageous. In order to assure rapid enough cooling ofwire, rod, sheet, strip, and other shapes in general, the mist densityadvantageously is high enough to cool whatever shape is aluminum coatedfrom the temperature it attains during coating (generally above 1250 F.)to below 1000 F. and preferably to below 900 F., in less than one-halfminute. Relatively massive articles will require times up to one-halfminute in the mist to be cooled to the extent indicated, whereas smalldiameter wires may be cooled to below 900 F. in a few seconds.

Thus the quenching efiiciency of the water mist is high and the aluminumcoating is rapidly congealed to a nonfiowing solid state. As a resultthe coating on the wire is held at substantially the thickness withwhich it is drawn from the aluminum bath 11, for it is solidified beforeit can become appreciably reduced in thickness by drainage down thewire. Moreover, the quenching effect of the mist congeals the aluminumcoating sufficiently rapidly so that uneven coating thickness and roughsurface characteristics are substantially avoided, even when the wire istravelling at its maximum velocity.

Although the aluminum coating layer is quite completely solidified uponcooling to a temperature below about 1200 F., the array of sprays 1'7,18 should be high enough tocool the wire as rapidly as possible to atemperature below 1000 F. and preferably below 900 F., so as to minimizethe thickness of brittle iron-aluminum alloy that forms byinterdiffusion of the ferrous metal wire and the aluminum coating. Ithas been found that the formation of such a brittle intermetalliccompound continues to occur even at temperatures substantially below thefreezing temperature of the aluminum layer. The rate at which such layerforms decreases with temperature, but the rate does not become verysmall until the temperature has been decreased to below about 1000 F.,and some formation of the intermetallic compound continues to occur bydiffusion until the wire has been cooled to below about 900 F.Accordingly, for optimum results a mist of the above specified densityshould be provided throughout the entire height of the array of sprays,and such height should be correlated with the maximum linear speed withwhich the wire W is passed through the apparatus, and with the thicknessof the wire, so that the temperature of the wire is reduced to below 900F. before the wire passes out of the mist formed by the sprays.Advantageously the height of the array of sprays is suflicient to effectcooling of the wire to a temperature even considerably below 900 F.before the wire passes beyond the spray zone, in order to be sure ofattaining the maximum benefits of the invention.

It is of course important that the sprays effect sufiicien-t cooling ofthe wire in the lower portion of the spray zone so that the coating onthe wire is fully solidified before it comes in contact with the dampingroll 36. 'Otherwise the damping roll will mechanically deform thecoating and thus lead to an inferior product.

As the wire passes out of the spray zone and over the head sheave 38, itis carried by the sinker sheave 40 to beneath the surface of the body ofliquid water in the quench tank 39. While quenching of the wire at thispoint is not necessary in accordance with the invention, it has theadvantage of insuring that the wire is brought to a temperature nearroom temperature preparatory to coiling and handling.

As an exmple according to the invention, a steel wire having a diameterof 0.132 inch has been provided with a heavy aluminum coating,approximately 0.0015 inch in thickness, by passing it at a velocity of115 feet per minute through a bath of molten aluminum containing 1.94%iron and 2.93% silicon, and then upwardly through a mist of waterdroplets of the size, velocity and density stated above, formed by anarray of water sprays of sufiicient height to quench and congeal thealuminum coating promptly and to cool the wire to the temperature below900 F. in a distance of approximately 24 feet from the point at whichthe wire emerged from the molten aluminum (i.e. within about 0.2 minute,or about 12 seconds, after emergence of the wire from the aluminumbath). The coating on the wire was sufiiciently adherent so that thewire could be wrapped on a mandrel of its own diameter without crackingor peeling of the coating. The coating moreover was quite uniform inthickness and exhibited smooth commercially acceptable surfacequalities. The wire could be drawn successfully to smaller sizes withoutdamaging the coating. The coating on the wire, as drawn, while thinnerthan when applied at larger diameter, was reasonably uniform, adherentand ductile and, therefore, commercially useful. An identical wirecoated in the same manner but cooled in air, without the rapid coolingattendant with the use of the water mist, had undesirable coatingcharacteristics in that the coating was more irregular and rough as wellas less adherent and more brittle. Moreover, the coating on this wire,after drawing to smaller size, was found to be non-adherent, brittleand, therefore, commercially unsatisfactory.

Although the invention has been particularly described above withreference to the coating of wires, it is of course apparent that themethod of the invention is equally applicable to coating other forms offerrous metal articles such as rod, sheet, strip, and other articles.

, It is also apparent that the apparatus described above can bemodified, without departing from the invention. For example, the spraynozzles 17, 18 instead of being all arranged on one side of the wire anddirected against a single splashboard, can be mounted so as to directthe sprays toward different faces of the article being coated. Inparticular, in coating sheet and strip, it is desirable to have spraysdirected against each side of the article as it emerges from the bath ofmolten aluminum. Likewise, although the method of the invention has beenparticularly described with reference to a continuous coating operation,it is equally applicable to batch coating operations in which articlesare dipped below the surface of the molten aluminum bath, and then, asthey are withdrawn from the coating bath and while the coating thereonis still fluid, are brought into direct contact with the liquid coolant.

I claim:

1. In a method for coating a ferrous metal shape with 9 aluminum "byimmersing the shape in a bath of molten aluminum and then withdrawingthe shape from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises introducing the coated shapeimmediately upon withdrawal from the aluminum bath and while thealuminum coating thereon is still fluid into direct contact with a densemist of liquid coolant, said mist comprising a gaseous suspension ofvery finely divided coolant droplets, the particle size of said dropletsbeing sufficiently small so that settlement thereof from suspension isnegligibly slow and the velocity with which said drop-lets impinge onsaid shape being sufficiently low so that substantially no deformationof the aluminum coating thereon while it is still fluid is causedthereby and the density of said mist being sulficient to cool analuminum coated wire 0.1 inch in diameter from 1250 F. to below 900 F.in less than fifteen seconds, whereby said coating is quenched andcongealed before flow of the molten coating metal can result in acoating having substantial irregularities in thickness and surfacesmoothness.

2. In a method for coating a ferrous metal shape with aluminum byimmersing the shape in a bath of molten aluminum and then withdrawingthe shape from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises bringing the coated shapepromptly after it emerges from the aluminum bath and while the coatingthereon is still in the fluid condition into direct contact with a densemist of liquid coolant, said mist comprising a gaseous suspension ofvery finely divided coolant droplets, the particle size of said dropletsbeing sufiiciently small so that settlement thereof rom suspension isnegligibly slow and the velocity with which said droplets impinge onsaid shape being sumciently low so that substantially no deformation ofthe aluminum coating thereon while it is still fluid is caused thereby,the density of said mist being sutficient to cool said coated article tobelow l000 F. in less than one-half minute, and maintaining the coatedshape in said mist until the temperature of said shape has been reducedto below 1000 F, whereby said coating is quenched and congealed beforeflow of the molten coating metal can lead to irregularities in thethickness and surface smoothness of the coating and whereby growth ofiron-aluminum alloy by interdiifusion of the coating and the ferrousmetal is minimized.

3. In a method for coating a ferrous metal shape with aluminum bycontinuously passing the shape into a bath of molten aluminum andcontinuously withdrawing the shape from the bath with a coating ofmolten aluminum adheringthereto, the improvement which comprisesbringing the coated shape promptly after it emerges from the aluminumbath and while the coating thereon is still in the fluid condition intodirect contact with a dense mist of liquid water, said mist comprising asuspension in air of water droplets of sufficiently small particle sizeso that settlement thereof from suspension does not occur to anysubstantial extent, and the velocity with which said droplets impinge onsaid shape being sufficiently low so that substantially no deformationof the aluminum coating prior to solidifying is caused thereby, thedensity of said mist being sufiicient to cool said coated article tobelow 900 F. in less than one-half minute, and maintaining the coatedshape in said mist until its temperature has been reduced to below 900F., whereby said coating is quenched and congealed before flow of themolten coating metal can lead to irregularities in the thickness andsurface smoothness of the coating and whereby growth of ironaluminumalloy by interdiifusion of the coating and the ferrous metal isminimized.

4. In a method for continuously coating ferrous metal wire, rod, sheet,strip, and other articles with aluminum by continuously passing sucharticle through a bath of molten aluminum and continuously withdrawingsuch article from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises delivering a dense mist of aliquid coolant into direct contact with the continuously moving articleimmediately upon its emergence from the bath of molten aluminum andwhile the aluminum coating thereon is still fluid, said mist comprisinga gaseous suspension of very finely divided coolant droplets, theparticle size of said droplets being sufliciently small so thatsettlement thereof from suspension is negligibly slow and the velocitywith which said droplets impinge on said shape being suificiently low sothat substantially no deformation of the aluminum coating thereon whileit is still fluid is caused thereby, and the'density of said mist beingsuflicient to cool an aluminum coated iron wire 0.1 inch in diameterfrom 1250 F. to below 900 F. in less than fifteen seconds, whereby saidcoating is quenched and congealed before flow of the molten coatingmetal on the continuously moving ferrous article can impart substantialirregularities to the thickness and surface smoothness of the coating.

5. In a method for continuously coating ferrous metal wire, rod, sheet,strip, and other articles with aluminum by continuously passing sucharticle through a bath of molten aluminum and continuously withdrawingsuch article from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises directing a fine mist of liquidwater into contact with the continuously moving article as it'emergesfrom the bath of molten aluminum and while the aluminum coating thereonis still at a temperature above 1200 F., said mist comprising asuspension in air of water droplets of sufliciently small particle sizeso that settlement thereof from suspension does not occur to anysubstantial extent, the velocity with which said droplets impinge onsaid shape being sufliciently low so that substantially no deformationof the aluminum coating prior to solidifying is caused thereby and thedensity of said mist being sufficient to cool said coated article tobelow 900 F. in less than one-half minute, and retaining the article insaid mist until the temperature of the article and of the coating hasbeen reduced to below 900 F., whereby said coating is quenched andcongealed before flow of the coating metal on the continuously movingferrous article can impart substantial irregularities to the thicknessand surface smoothness of the coating, and whereby growth ofiron-aluminum alloy by interdilfusion of the coating and the ferrousmetal is minimized.

6. In a method for continuously coating ferrous metal wire, rod, sheet,strip, and other articles with aluminum by continuously passing sucharticle through a bath of molten aluminum and continuously withdrawingsuch article from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises continuously withdrawing thearticle upwardly from the molten aluminum bath in a substantiallyvertical direction, and spraying a fine mist of a liquid coolant on tothe upwardly moving article promptly after its emergence from said bathand while the coating thereon is still fluid, said mist comprising agaseous suspension of liquid coolant droplets in which the particle sizeof the droplets is sufficiently small so that they tend to settle fromsuspension only very slowly, and said mist being directed into contactwith the article in the form of a wide-angle spray the velocity of whichas it impinges on the upwardly moving article is sufliciently low sothat substantially no deformation of the aluminum coating is causedthereby, and the density of said mist being sufiicient to cool analuminum coated iron wire 0.1 inch in diameter from 1250 F. to below 900F. in less than fifteen seconds, whereby said coating is quenched andcongealed before flow of the molten coating metal on the continuouslymoving ferrous article can impart substantial irregularities to thethickness and surface smoothness of the coating.

7. In a method for continuously coating ferrous metal wire, rod, sheet,strip, and other articles with aluminum by continuously passing sucharticle through a bath of molten aluminum and continuously withdrawingsuch article from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises continuously withdrawing theferrous article upwardly from the aluminum bath in a substantiallyvertical direction, spraying a fine mist of water droplets on to theupwardly moving article promptly after its emergence from said bath andwhile the coating thereon is still fluid, said mist comprising an airsuspension of liquid water droplets of sufiiciently small particle sizeso that settlement thereof does not occur to any substantial extent,said mist being delivered into contact with the article in the form of awide-angle spray of such low velocity where it impinges on the upwardlymoving article that substantially no deformation of the aluminum coatingis caused thereby, the density of said mist being sufiicient to coolsaid coated article to below 900 F. in less than one-half minute, andmaintaining the advancing article in the water mist spray until thetemperature of the article and of the coating has been reduced to below900 E, whereby said coating is quenched and congealed before flow of thecoating metal on the continuously moving ferrous article can impartsubstantial irregularities to the thickness and surface smoothness ofthe coating, and whereby growth of iron-aluminum alloy by interdiffusionof the coating and the ferrous metal is minimized.

8. In a method for continuously coating ferrous metal, wire, rod, sheet,strip and other articles with aluminum by continuously passing sucharticle through a bath of molten aluminum and continuously withdrawingsuch article from the bath with a coating of molten aluminum adheringthereto, the improvement which comprises delivering a dense mist of aliquid coolant into direct contact with the continuously moving articleimmediately upon its emergence from the bath of molten aluminum andwhile the aluminum coating thereon is still fluid, said mist comprisinga gaseous suspension of very finely divided coolant droplets, theparticle size of said droplets being sufliciently small so thatsettlement thereof from suspension is negligibly slow and the velocitywith which said droplets impinge on said shape being sufiiciently low sothat substantially no deformation of the aluminum coating thereon Whileit is still fluid'is caused thereby, said mist comprising a plurality ofsprays from a plurality of point sources so spaced that there issubstantially no overlap of spray delivered from one point source withthe spray delivered from an adjacent source at the point where saidsprays meet the path of travel of said continuously moving article, thedensity of said mist being sufficient to cool said coated article tobelow 1000 F. in less than one-half minute, and maintaining the coatedarticle in said mist until the temperature thereof has been reduced tobelow 1000 F., whereby said coating is quenched and congealed before theflow of the molten coating metal on the continuously moving ferrousarticle can impart substantial irregularities to the thickness andsurface smoothness of the coating and whereby growth of iron-aluminumalloy by interdilfusion of the coating and the ferrous metal isminimized.

9. Apparatus for coating ferrous metal wire, rod, sheet, strip, andother articles with aluminum, comprising a vessel for containing a bathof molten aluminum, means for continuously passing such article throughsaid bath and for withdrawing the article upwardly from the moltenaluminum bath through a substantially vertical path of travel, an arrayof atomizing spray nozzles arranged in vertically spaced relation andall directed at said path of travel, the lowermost of said nozzles beingdirected at said path of travel in the region thereof immediately abovesaid vessel and the uppermost of said nozzles being directed at saidpath of travel at a substantial distance above said vessel and theintermediate nozzles being spaced so that substantially the entirelength of said path of travel between the lowermost and uppermostnozzles is covered by spray therefrom, means for delivering a liquidcoolant to said spray nozzles, and means connecting said nozzles with asource of atomizing gas under pressure, whereby said coolant may bedischarged from said nozzles in the form of a mist of particles so smallthat settlement thereof from gaseous suspension is negligibly slow.

10. Apparatus for coating ferrous metal wire, rod, sheet, strip, andother articles with aluminum, comprising a vessel for containing a bathof molten aluminum, means for continuously passing such article throughsaid bath and for withdrawing the article upwardly from the moltenaluminum bath through a substantially vertical path of travel, an arrayof atomizing spray nozzles arranged in vertically spaced relation andall directed at said path of travel, the lowermost of said nozzles beingdirected at said path of travel in the region thereof immediately abovesaid vessel and the uppermost of said nozzles being directed at saidpath of travel at a substantial distance above said vessel and theintermediate noz zles being spaced so that substantially the entirelength of said path of travel between the lowermost and uppermostnozzles is covered by spray therefrom, means for delivering a liquidcoolant to said spray nozzles, and means connecting said nozzles With asource of atomizing gas under pressure, whereby said coolant may bedischarged from said nozzles in the form of a mist of particles so smallthat settlement thereof from gaseous suspension is negligibly slow, saidnozzles being so arranged that there is substantially no overlap of thespray delivered from one nozzle with the spray delivered from anadjacent nozzle where said sprays meet the path of travel of saidarticle.

References Cited in the file of this patent UNITED STATES PATENTS1,863,809 Hapkins June 21, 1932 2,034,348 Lytle Mar. 17, 1936 2,069,658Renkin- Feb. 2, 1937 2,126,244 Cook Aug. 9, 1938 2,166,510 Whitfield eta1. July 18, 1939 2,243,979 Reynolds June 3, 1941 2,569,097 Grange Sept.25, 1951

1. IN A METHOD FOR COATING A FERROUS METAL SHAPE WITH ALUMINUM BYIMMERSING THE SHAPE IN A BATH OF MOLTEN ALUMINUM AND THEN WITHDRAWINGTHE SHAPE FROM THE BATH WITH A COATING MOLTEN ALUMINUM ADHERING THERETO,THE IMPROVEMENT WHICH COMPRISES INTRODUCING THE COATED SHAPE IMMEDIATELYUPON WITHDRAWAL FROM THE ALUMINUM BATH AND WHILE THE ALUMINUM COATINGTHEREON IS STILL FLUID INTO DIRECT CONTACT WITH A DENSE MIST OF LIQUIDCOOLANT, SAID MIST COMPRISING A GASEOUS SUSPENSION OF VERY FINELYDIVIDED COOLANT DROPLETS, THE PARTICLE SIZE OF SAID DROPLETS BEINGSUFFICIENTLY SMALL SO THAT SETTLEMENT